With regard to a communications system, a point-to-point connection is a connection in which information is transported between two nodes or endpoints. Modernly, there is a need to transport digitally encoded information such as video, voice and data signals over relatively long distances using a point to point connection. In this regard, optical fibers can be used to transport signals over relatively long distances with relatively low signal distortion or attenuation, as compared with copper wire or co-axial cables.
One way to transport digital information across an optical fiber is to encode the digital signal on an analog signal (e.g. RF signal) using a modem. Next, the RF signal can be converted into a light beam signal using an optical transmitter such as a laser diode, and then introduced into an end of an optical fiber. In this process, more than one light signal can be transmitted at one time. Typically, to accommodate the transport of a large volume of information, a relatively large bandwidth RF signal, having a multi-octave bandwidth, is converted and transmitted over the optical fiber. For these multi-octave optical transmissions, composite second order distortions caused by fiber dispersion can cause significant signal degradation at optical transport distances of about 1 km, or more.
One solution to the limitations associated with composite second order distortions is to use an RF signal having a sub-octave bandwidth. For example, U.S. patent application Ser. No. 12/980,008 for an invention titled “Passive Optical Network with Sub-Octave Transmission,” which is owned by the same assignee as the present invention, and which is incorporated herein by reference, discloses that the unwanted second order distortions in a transmitted optical signal can be significantly reduced in a passive optical network when the radio frequency carriers are selected from a sub-octave bandwidth. Further, with a frequency up-conversion for the transmission of signals in a sub-octave band, frequency interferences in multi-wavelength optical transmissions can be avoided.
In light of the above, it is an object of the present invention to provide a system and method for optically transporting a plurality of digital signals over a single optical fiber over distances greater than about 1 km. Another object of the present invention is to provide a system and method for reducing the adverse effects of composite second order distortions during transport of a plurality of digital signals over a point to point communications connection. Still another object of the present invention is to provide a system and method for using frequency conversions for sub-octave transmission of signals over a fiber optic that are easy to use, relatively easy to manufacture, and comparatively cost effective.